DOI: 10.1002/cssc.201402999 Direct Alcohol Fuel Cells: Toward the Power Densities of Hydrogen-Fed Proton Exchange Membrane Fuel Cells Yanxin Chen, [a, b] Marco Bellini, [a] Manuela Bevilacqua, [a] Paolo Fornasiero, [b] Alessandro Lavacchi, [a] Hamish A. Miller,* [a] Lianqin Wang, [a, b] and Francesco Vizza* [a] Introduction The growing limitation of world fossil fuel reserves together with a huge increase in global energy consumption has accel- erated both academic and industrial interest in the exploitation of renewable fuel resources. [1] Renewable fuels such as bio- mass-derived alcohols are attractive alternatives to methanol in direct fuel cells because of their low toxicity and well-estab- lished distribution infrastructure. [2] Among these ethanol (EtOH) is the most promising because of the possibility for its production from the fermentation of biomass or the steam re- forming of lignocelluloses with reasonably low energy cost. [3] Alcohols with a higher molecular weight are also attracting at- tention as they offer high energy densities, low vapor pressure, and some of them can be obtained from renewable resources. Included in this group are ethylene glycol [4] (EG) and glycerol [5] (G). EG has a volumetric energy density of 5.9 kWh L À1 and can be produced by the heterogeneous hydrogenation of cellulose derivatives. [6] G has a volumetric energy density of 6.3 kWh L À1 , is a byproduct of biodiesel production, and, as such, is inex- pensive (0.3 US$ kg À1 ) and readily available (2.4 million tonnes produced per year). [7] The exploitation of these biomass-de- rived alcohols in direct fuel cells is an attractive and simple way to transform their chemical energy into electrical power. Recently, anion exchange membrane (AEM) direct alcohol fuel cells (DAFCs) have attracted much attention (Figure 1). [2b, 8] In alkaline media the kinetics of the oxygen reduction reaction (ORR) are greatly enhanced because of improved charge trans- fer. [2a] The high pH also offers a much less corrosive environ- ment and hence nonprecious metal catalysts such as Fe/C, FeCo/C, and FeAg/C can be employed at the cathode. [9] Polari- zation losses caused by alcohol crossover from the anode to the cathode are also alleviated by using these catalysts, which are highly selective for the ORR. A2 mm thick layer of TiO 2 nanotube arrays was prepared on the surface of the Ti fibers of a nonwoven web electrode. After it was doped with Pd nanoparticles (1.5 mg Pd cm À2 ), this anode was employed in a direct alcohol fuel cell. Peak power densi- ties of 210, 170, and 160 mW cm À2 at 80 8C were produced if the cell was fed with 10 wt % aqueous solutions of ethanol, ethylene glycol, and glycerol, respectively, in 2 m aqueous KOH. The Pd loading of the anode was increased to 6 mg cm À2 by combining four single electrodes to produce a maximum peak power density with ethanol at 80 8C of 335 mW cm À2 . Such high power densities result from a combination of the open 3 D structure of the anode electrode and the high electro- chemically active surface area of the Pd catalyst, which pro- mote very fast kinetics for alcohol electro-oxidation. The peak power and current densities obtained with ethanol at 80 8C ap- proach the output of H 2 -fed proton exchange membrane fuel cells. Figure 1. Schematic representation of a DAFC fueled with ethanol operating with an anion exchange membrane and KOH electrolyte. [a] Dr. Y. Chen, M. Bellini, Dr. M. Bevilacqua, Dr. A. Lavacchi, Dr. H. A. Miller, L. Wang, Dr. F. Vizza Institute of Chemistry of Organometallic Compounds ICCOM-CNR, Polo Scientifico Area CNR Via Madonna del Piano 10, 50019 Sesto Fiorentino (Italy) E-mail : hamish.miller@iccom.cnr.it [b] Dr. Y. Chen, Dr. P. Fornasiero, L. Wang Department of Chemical and Pharmaceutical Sciences ICCOM-CNR Trieste Research Unit University of Trieste Via L. Giorgieri, 1 34127 Trieste (Italy) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201402999.  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemSusChem 0000, 00, 1 – 11 &1& These are not the final page numbers! ÞÞ CHEMSUSCHEM FULL PAPERS